Facsimile and static presentation processing – Facsimile – Specific signal processing circuitry
Patent
1985-01-10
1987-05-19
Chin, Tommy P.
Facsimile and static presentation processing
Facsimile
Specific signal processing circuitry
358905, 455296, H04N 521
Patent
active
046672419
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a ghost cancelling system for cancelling out a ghost at a stage of, for example, a video signal.
BACKGROUND ART
The following ghost cancelling system has been proposed in the prior art. As, for example, shown in FIG. 1, a signal received by an antenna 1 is supplied through a tuner 2 and a video intermediate frequency amplifier 3 to a video detector circuit 4 which then detects a video signal. This video signal is supplied through a delay circuit 5 with a delay time corresponding to the eliminating period of a pre-ghost to a composer 6 and a ghost cancelling signal imitating the ghost derived from a transversal filter that will be described later is supplied to the composer 6 so that the video signal with the ghost cancelled out is delivered from the composer 6 to an output terminal 7.
The video signal derived from the video detector circuit 4 is supplied to a delay circuit 8 that forms a part of the transversal filter. In this delay circuit 8, delay elements, each of which takes a sampling period (for example, 10 [ns] (nano seconds)) as a unit of delay, are connected in a plurality of stages (n number) to establish a delay time equal to the eliminating period of the pre-ghost and, n taps are led out from the respective stages. The signals from these n taps are respectively supplied to weighting circuits 9.sub.1, 9.sub.2, . . . 9.sub.n each of which is formed of a multiplier.
The signal from the end of the delay circuit 8 is supplied to a terminal 10f of a mode switch 10 and the output signal from the composer 6 is supplied to the other terminal 10b of the mode switch 10. The signal derived from this mode switch 10 is supplied to a delay circuit 11. This delay circuit 11 is formed of delay elements, each delay element taking a sampling period as a unit delay time, connected in a plurality of stages (m number) to have a delay time equal to an eliminating period of a delay-ghost and m taps are led out from the respective stages thereof. The signals from these taps are respectively supplied to weighting circuits 12.sub.1, 12.sub.2, . . . 12.sub.n, each of which is formed of a multiplier.
The video signal from the composer 6 is supplied to a subtracting circuit 13. Further, the video signal from the delay circuit 5 is supplied to a synchronizing separator circuit 14 and the separated synchronizing signal therefrom is fed to a standard wave forming circuit 15 and a low-pass filter 16 by which a standard waveform approximate to a step-waveform of a rising edge VE of the vertical synchronizing signal is formed. This standard waveform is supplied to the subtracting circuit 13.
The signal from this subtracting circuit 13 is supplied to a differentiation circuit 17 which then detects the ghost.
For the ghost detecting signal, there is employed such a signal that is contained in a standard television signal and which is not affected by other signals during the period as long as possible, for example, the vertical synchronizing signal. That is, as shown in FIG. 2, the periods .+-.1/2 H (H is the horizontal period) before and after the rising edge VE of the vertical synchronizing signal are not affected by other signals. Therefore, the afore-noted standard waveform is subtracted from the signal in this period and the subtracted signal is differentiated to thereby detect a weighting factor.
When there is contained a ghost with a phase difference of 45.degree. from a desired signal and with a delay time .tau.(=.omega..sub.c .tau. where .omega..sub.c is the video carrier angular frequency in the high frequency stage), the video signal with the waveform as shown in FIG. 3A appears. While, if this signal is differentiated and inverted in polarity, a ghost detecting signal with a differentiation waveform as shown in FIG. 3B is provided. This differentiation waveform can approximately be regarded as an impulse response to the ghost.
The ghost detecting signal of the differentiation waveform appearing from the differentiation circuit 17 is supplied through an amplifier 18 to demulti
REFERENCES:
patent: 4344089 (1982-08-01), Ustunomiya
patent: 4357631 (1982-11-01), Utsunomiya
patent: 4517601 (1985-05-01), Yamada
Saito Jun'ya
Tsutsui Ichiro
Yamada Hisafumi
Chin Tommy P.
Sony Corporation
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